The present invention is directed to seat support mechanisms for tiltable chairs of the type commonly found in offices. Numerous arrangements of this type are found in the prior art U.S. Pat. Nos. 2,991,125, 3,131,904, 3,480,249, 3,592,433, 3,868,144, 4,295,626 and 4,718,726. None of these arrangements disclose the features of the present invention.